To study changes in the incidence of obstetric anal sphincter rupture (OASR) during recent years in Denmark, Finland, Sweden and Norway and hospital-based incidence in recent years in Norway.
Retrospective birth register study.
Unselected population of delivering women in four Nordic countries.
All deliveries (574 175) registered in Denmark, Finland, Norway and Sweden, 2004-2010.
Parity data, including maternal, obstetrical and fetal characteristics, were obtained. The incidence of OASR was calculated from vaginal deliveries. A chi-squared test was used to analyse differences between countries and time periods.
Incidence of OASR.
During the study period, the OASR incidence in Finland was notably lower (0.7-1.0%) than in the other three Nordic countries (4.2-2.3%). A significant and constant reduction in OASR incidence was observed in Norway only (from 4.1 to 2.3%, from 2004 to 2010, p